1. Field of the Invention
The present invention relates to an insulating gas for an electric device having increased insulating strength.
2. Description of the Prior Art
Recently, there has been adopted a method in which sulfur hexafluoride gas (hereinafter referred to as "SF.sub.6 gas") is filled in a vessel in which an electric device is disposed, as shown in FIG. 1, whereby good insulating properties are maintained and the size of the electric device is decreased. In FIG. 1, reference numeral 1 represents a vessel, reference numeral 2 represents SF.sub.6 gas which fills the vessel 1, reference numeral 3 represents a bushing, reference numeral 4 represents a disconnecting portion, reference numeral 5 represents a breaking portion, and reference numeral 6 represents a conductor connecting the disconnecting portion 4 to the breaking portion 5.
Accordingly, in a gas-insulated electric device having a live part supported by a solid insulating member, such as a gas-insulated switch or bus bar, the size of the electric device is diminished and the reliability is improved, and the device is made more suitable for use in its environment.
However, further reductions in size are desired because of increased demand for electric power or because of problems related to land shortages, and use of a gas having better insulating properties than SF.sub.6 gas is now considered.
Pentafluoropropionitrile (hereinafter referred to as "C.sub.2 F.sub.5 CN") is one example of a gas having a higher insulating strength than SF.sub.6 gas. It has an insulating strength 1.8 times as high as that of SF.sub.6 gas and it is a chemically stable compound. Accordingly, it is considered that C.sub.2 F.sub.5 CN is promising as an insulating gas for electric devices.
However, since C.sub.2 F.sub.5 CN has not been actually used, the effects of this gas on humans are not known, and if C.sub.2 F.sub.5 CN remains in the vessel, safety and sanitation problems can arise when the electric device is checked.